Method and apparatus for manufacturing tubes

ABSTRACT

A method for manufacturing a tube made of a non-ferrous material, particularly a tube made of mainly copper, in which method, in the first working step the tube billet ( 1 ) is worked so that mainly owing to the deformation resistance, the temperature of the tube billet under operation rises up to the recrystallization range, at least on the spot that is being worked. Essentially immediately after the first working step (F 1 ), the tube billet is subjected to at least a second working step (F 2 ), and the tube billet ( 1 ) is maintained, at least during the first and second working step in non-oxidizing conditions. The invention also relates to an apparatus.

[0001] The present invention relates to a method according to thepreamble of claim 1 for manufacturing tubes. The invention also relatesto an apparatus according to claim 15.

[0002] From the U.S. Pat. No. 4,876,870, there is known a method formanufacturing tubes of a non-ferrous metal, where a continuously castbillet is cold worked for instance by planetary rolling, so that owingto the influence of deformation resistance, the temperature of theworked material rises to the recrystallization range. In saidpublication, cold working generally means a process where thetemperature of the billet under operation is normal when staring theworking, but rises along with the process essentially higher than in anordinary cold working operation, i.e. up to the recrystallization rangeof the material. A planetary rolling arrangement suited to implementinga prior art method is disclosed in the U.S. Pat. No. 3,735,617, wherethree conical rolls are arranged at angles of 120° with respect to eachother. The rolls rotate both around their own axis and around the centerof the planetary housing. In said arrangement, the mainly conicallynarrowing shape of the rolls is essentially narrowed in the proceedingdirection of the material to be rolled. There are also knowncorresponding planetary rolling arrangements, particularly applied inthe rolling of steel tubes, where the rolls are arranged in a reversedposition with respect to the proceeding direction of the rolledmaterial, in which case their conical shape is narrowed against theproceeding direction of the material to be rolled.

[0003] The U.S. Pat. No. 4,510,787 introduces a method for manufacturinghollow rods, where one possibility is to employ mainly conical rollsthat are narrowed in an opposite direction than the proceeding directionof the rolled material. Copper tubes have been manufactured extremelysuccessfully by using the method of the prior art. However, ifproduction capacity should be increased, the current method andparticularly the employed equipment have some drawbacks. An increase inthe production capacity requires an increase in the rolling speed. Thestructures of current rolling mills, particularly the structures of theroller heads, are ill suited to increasing the rolling speed and therolling mill rotation speed. This is due to the influence of centrifugalforces, among others.

[0004] The object of the invention is to realize a method wherebyproduction capacity can be increased economically. Another object of theinvention is to realize an apparatus whereby the drawbacks of the priorart can be avoided and production capacity increased.

[0005] The invention is based on the observation that the workingresistance of copper is diminished to a fraction afterrecrystallization. This enables an extremely economical further workingof the tube billet with an equipment that is remarkably more economicalthan in the first working step.

[0006] The invention is characterized by what is set forth in theclaims.

[0007] The method according to the invention has several remarkableadvantages. The division of the working process into two steps enables,among others, after the first working step, a larger wall thickness ofthe tube billet than in the method of the prior art, which results in anincrease in the production capacity. The working of the tube billetwhich is in the first working step recrystallized and softened in thesecond working step immediately after the first working step onlyrequires a slight amount of power of the working arrangement. Moreover,the invention enables extremely versatile working conditions in thesecond working step. The second working step can be carried out with oneor several roll arrangements. There can be applied planetary rolling,stretch reducing or sizing rolling. Apart from diminishing the tubebillet diameter, said diameter can also be enlarged in the secondworking step. Optimal conditions for the working steps are achieved byadjusting the tube billet temperature.

[0008] In the present application, a conical roll generally means arolling mill roll with a diameter that is at the rolling surface, at thefirst end of said rolling surface, larger than at the second end. Thetrue shape of the conical roll does not necessarily have to be conicalor frusto-conical, but it can be varied according to the particularembodiment. Planetary rolling generally means rolling where the rollsrotate both around their own axis and around the billet to be rolled.

[0009] The invention is explained in more detail below, with referenceto the appended drawings, where

[0010]FIG. 1 is a simplified illustration of a prior art arrangement,

[0011]FIG. 2 is a simplified illustration of a method according to theinvention, and

[0012]FIG. 3 illustrates a detail of an embodiment according to theinvention.

[0013]FIG. 1 illustrates a prior art solution for working a tube billet1 by rolling. In the prior art arrangement, the tube billet 1 isplanetary rolled in one working step mainly with conical roll elements2, which will be called conical rolls in the text below. Each of theconical rolls 2 rotates around its rotary axis 3, and in addition, therolls typically rotate essentially around the rotary axis of theplanetary housing, which axis is parallel to the central axis 4 of thetube billet. During rolling, there is typically used a mandrel 5 insidethe tube billet. In the drawing, the motional direction of the tubebillet is indicated by the arrow 6. For the sake of clarity, the movingand drive gear of the conical rolls 2 is left out of the drawing. Sometypical rolling arrangements utilizing conical rolls are disclosed forinstance in the publications U.S. Pat. No. 3,735,617 and GB 2019281 A.

[0014]FIG. 2 is a simplified illustration of an embodiment according tothe method of the present invention, shown in cross-section along theline A-A of FIG. 1.

[0015] Accordingly, for example a continuously cast tube billet 1 isbrought to a working step according to the invention. In the firstworking step F₁ of the method, the tube billet is worked so that thetemperature of the tube billet to be worked rises, mainly owing to theinfluence of deformation resistance, up to the recrystallization rangeor in the vicinity thereof, at least in the spot that is being worked.The first working step F₁ is carried out by a first rolling mill device.The first rolling mill device includes at least one, preferably severalrolls 2. In the embodiment of FIG. 2, the conical rolls 2 rotate aroundtheir axis 3 and also around the center of the planetary housing, forinstance, which housing is typically located on the central axis 4 ofthe tube billet 1. Inside the tube billet 1, there is typically employeda mandrel 5, in which case the wall of the tube billet 1 is workedbetween the rolls 2 and the mandrel 5. Typically, in the first workingstep, the degree of working, the wall thickness of the tube billet underoperation and the mass flow are chosen so that there is achieved amaximum mass flow, and that there are good conditions forrecrystallization. Typically the tube billet is cold worked in the firstworking step.

[0016] Essentially immediately after the first working step F₁, the tubebillet is subjected to a second working step F₂. At least during thefirst working step F₁ and the second working step F₂, and advantageouslyalso between said working steps, the tube billet 1 is kept innon-oxidizing conditions. Said non-oxidizing conditions are created forinstance by means of a protective gas space 9, where the conditions areadjusted in order to at least partly prevent the oxidation of the tubebillet. The employed protective gas can typically be for examplenitrogen or argon.

[0017] According to a preferred embodiment of the method according tothe invention, in the second working step F₂ the wall thickness s of thetube billet 1 is diminished. Typically the wall thickness of the tubebillet 1 is diminished for about 50-70% in the second working step F₂.The second working step F₂ may comprise several successive rollingsteps. In a typical embodiment, in the second working step F₂ the tubebillet 1 is worked by planetary skew rolling or planetary cross-rolling.In another embodiment, in the second working step F₂ the tube billet 1is worked by stretch reducing. In a third embodiment, the tube billet isworked by applying sizing rolling. Different types of working processescan also be combined in succession.

[0018] The method according to the invention provides widerpossibilities for working than the prior art. In the second working stepF₂, the (inner) diameter d of the tube is maintained essentiallyconstant. In another preferred embodiment, the tube diameter d isenlarged in the second working step F₂ (FIG. 3). The tube diameter d isenlarged by using, when necessary, a mandrel 5 inside the tube billet.In FIG. 3, the diameter of the mandrel 5 is enlarged at the secondworking spot conically towards the output direction 6 of the tubebillet. In a typical case, the wall thickness s of the tube billet issimultaneously diminished. In a preferred embodiment, the tube billetdiameter d can also be diminished in the second working step F₂.

[0019] In the method according to the invention, the (inner) diameter dand the wall thickness s of the tube billet can be adjusted to thedesired measures in a way that is remarkably more flexible than thoseused in the prior art, without having to restrict the capacity.

[0020] When necessary, the temperature of the tube billet is adjusted,either prior to the first working step, during it, prior to the secondworking step or during it. Heating can be carried out for instance byusing an induction coil. Naturally the billet can also be cooled.

[0021] The apparatus according to the invention for working the tubebillet comprises in the first working step F₁ a rolling mill arrangementwith at least one roll element 2. Essentially immediately after therolling arrangement of the first working step F₁, in the proceedingdirection 6 of the tube billet 1, there is arranged the rollingarrangement of the second working step F₂. The apparatus includes aprotective gas space 9 for protecting the tube billet 1, at least at thefirst working step F₁ and the second working step F₂ of the rollingarrangement and advantageously also therebetween.

[0022] Typically the protective gas space 9 surrounds, at least partly,the rolling arrangement of both the first and the second working step,and also the space provided in between, at least in the vicinity of thetube billet 1.

[0023] In a typical embodiment, the diameter of the roll element of therolling arrangement of the first working step F₁ is larger on the inputside of the tube billet than on the output side (as is seen in FIG. 1).According to another embodiment, the diameter of the roll element 2 ofthe first rolling arrangement is larger on the tube billet output sidethan on the tube billet input side (according to FIG. 2). Typically thefirst rolling arrangement is a planetary mill with at least threeconical roll elements 2 provided as the employed rolling elements.

[0024] In the embodiment of FIG. 2, at least one of the rollingarrangements of the second working step F₂ is a planetary mill.

[0025] In a preferred embodiment, the rotary axis 8 of the roll 7 of therolling arrangement of the second working step is parallel to thelongitudinal axis 4 of the tube billet 1.

[0026] Typically the rotary axis 8 of at least one roll 7 of the rollingarrangement of the second working step forms an angle with thelongitudinal axis 4 of the tube billet.

[0027] In an embodiment, the rotary axis 8 of at least one roll 7 of therolling arrangement of the second working step is essentiallyperpendicular to the plane that is tangential to the longitudinal axis 4of the tube billet 1.

[0028] Thus the roll arrangement of the rolling apparatus of the secondworking step can consist of conical roll elements, or roll elements withrotary axes that are perpendicular to the proceeding direction of thetube billet, or of a combination of these.

[0029] The apparatus comprises at least one mandrel element 5. The shapeand size of said mandrel element depends on the embodiment in question.FIG. 3 illustrates an embodiment where the (inner) diameter d of thetube billet 1 is diminished. At the same time, the wall thickness s ofthe tube billet 1 is diminished. The diameter of the mandrel 5 isdiminished conically at the working spot towards the output direction 6of the tube billet 1.

[0030] The invention is mainly suited to the manufacturing of tubes madeof a nonferrous material. In particular, the invention is designed tothe manufacturing of copper or copper alloy tubes.

1. A method for manufacturing a tube made of a non-ferrous material,particularly a tube made of mainly copper, in which method in the firstworking step a tube billet (1) is worked, so that mainly owing todeformation resistance, the temperature of the tube billet underoperation rises up to the recrystallization range, at least on theworking spot, characterized in that essentially immediately after thefirst working step (F₁), the tube billet (1) is subjected to a secondworking step (F₂), and that at least during the first and second workingstep, the tube billet (1) is kept in non-oxidizing conditions.
 2. Amethod according to claim 1, characterized in that the tube billet iskept in non-oxidizing conditions also between the first and secondworking step.
 3. A method according to claim 1 or 2, characterized inthat the non-oxidizing conditions are provided by means of a protectivegas chamber (9) which contains protective gas.
 4. A method according toany of the claims 1-3, characterized in that in the first working step(F₁) the tube billet (1) is cold worked.
 5. A method according to any ofthe claims 1-4, characterized in that the wall thickness (s) of the tubebillet (1) is diminished in the second working step (F₂).
 6. A methodaccording to any of the claims 1-5, characterized in that wall thickness(s) of the tube billet (1) is diminished for about 50-70% in the secondworking step (F₂).
 7. A method according to any of the claims 1-6,characterized in that the diameter (d) of the tube billet (1) is keptessentially constant in the second working step (F₂).
 8. A methodaccording to any of the claims 1-7, characterized in that the diameter(d) of the tube billet (1) is diminished in the second working step(F₂).
 9. A method according to any of the claims 1-8, characterized inthat the diameter (d) of the tube billet (1) is enlarged in the secondworking step (F₂).
 10. A method according to any of the claims 1-9,characterized in that the second working step (F₂) is carried out byrolling with at least one roll (7).
 11. A method according to any of theclaims 1-10, characterized in that in the first working step (F₁), thetube billet (1) is rolled, particularly with conical rolls (2).
 12. Amethod according to any of the claims 1-11, characterized in that thetube billet is worked at least in one of the working steps (F₁, F₂) byrolling, particularly by planetary rolling.
 13. A method according toany of the claims 1-12, characterized in that the tube billet (1) is acontinuously cast billet.
 14. A method according to any of the claims1-13, characterized in that the temperature of the tube billet (1) isadjusted when necessary.
 15. An apparatus for working a tube billet (1),said apparatus comprising a planetary arrangement including at least oneroll element for performing the first working step (F₁), characterizedin that essentially immediately after the first rolling arrangement, inthe proceeding direction (6) of the tube billet (1), there is arranged asecond rolling arrangement in order to provide for at least one secondworking step (F₂), and that there are provided means for creatingnon-oxidizing conditions, so that at least during the first and secondrolling step (F₁, F₂) the tube billet (1) is kept in non-oxidizingconditions.
 16. An apparatus according to claim 15, characterized inthat the means for creating non-oxidizing conditions comprise at leastone protective gas chamber (9).
 17. An apparatus according to claim 15or 16, characterized in that the protective gas chamber (9) surroundsthe first and second rolling arrangement and the space providedtherebetween at least in the vicinity of the tube billet (1).
 18. Anapparatus according to any of the claims 15-17, characterized in thatthe diameter of the conical roll element (2) of the first rollingarrangement is, in the proceeding direction (6) of the tube billet,larger on the input side than on the output side.
 19. An apparatusaccording to any of the claims 15-17 characterized in that the diameterof the conical roll element (2) of the first rolling arrangement is, inthe proceeding direction (6) of the tube billet, larger on the outputside than on the tube billet input side.
 20. An apparatus according toany of the claims 15-19, characterized in that the first rollingarrangement is a planetary mill, where at least three conical rollelements (2) are provided as rolling elements.
 21. An apparatusaccording to any of the claims 15-20, characterized in that at least oneother rolling arrangement is a planetary mill.
 22. An apparatusaccording to any of the claims 15-21, characterized in that the rotaryaxis (8) of at least one roll (7) of the second rolling arrangementforms an angle with the longitudinal axis (4) of the tube billet.
 23. Anapparatus according to any of the claims 15-22, characterized in thatthe rotary axis (8) of the roll (7) of the second rolling arrangement isparallel with the longitudinal axis (4) of the tube billet (1).
 24. Anapparatus according to any of the claims 15-23, characterized in thatthe rotary axis (8) of at least one roll (7) of the second rollingarrangement is essentially perpendicular to a plane that is tangentialto the longitudinal axis (4) of the tube billet (1).
 25. An apparatusaccording to any of the claims 15-24, characterized in that theapparatus comprises at least one mandrel element (5).